The Running Gait, Part 1: Contralaterality

All gait is a contralateral movement. Although It seems like the most obvious statement (perhaps to the point of being boring), it often astonishes me just how unexamined it remains. Discussing both the theoretical and practical implications—what it means for our training—is what this series of posts is all about.

To say that a movement is contralateral is to say that when something happens in one side, the opposite will happen in the other side. During gait, if our left leg moves forward, our right leg moves back. But our gait is also reciprocal, meaning that the limbs in the same side move in opposition to each other, to balance their movement. If our right leg, supporting our body during the stance phase of gait, moves back, our right arm swings forward in a passive motion meant to balance out this movement.

This kind of reciprocal action is very similar to the kind of activity that you find in a lot of modern machines. Let’s take the internal combustion engine as an example. To make this simple, let’s look at a flat twin engine like the one mounted on a lot of BMW motorcycles:


In the image you can see two pistons, each moving in opposition to each other around a crankshaft. This movement is—or should be—a lot like the movement of the legs around the hips. By the way, this imagery isn’t just a metaphor: there are important similarities between the mechanics of the piston system and the mechanics of the hips and legs.

I liken the lowest point in the piston’s rotation to when the leg (the right) is in swing (1). The apex of the piston’s upswing corresponds to midstance, where one leg (the right) is fully supporting the body (2). At the same moment, an opposing piston must be in the lowest point of its downswing in order to balance the mechanism.

Piston Mo
By Zephyris – Own work, CC BY-SA 3.0,

Any problems in the balance of the pistons or the crankshaft can cause something to go horribly wrong. The same goes for the body, in order for its movement to be in balance. As the left leg clears the ground behind the body, the right (opposite) arm must be ready to initiate the upswing. And the right leg should be ready to start reaching for the ground below.

Insofar this is the case, the movement can be said to be contralateral.

Let’s look at the pictures of Mo again (taken as he is sprinting down the final stretch of his gold-medal performance in the 10,000 meter event of the 2012 Olympics). As you can see from the right arm in (1) and the left arm in (2), both pictures are taken at the same moment in gait (from the frame of reference of the arms).


By comparing both pictures you can see a bit more flexion in early stance for the left leg (1), than for the right leg (2). At this moment in gait, the right leg trails further behind the body (1) than the left leg. (The left calf (1) is also at a larger angle than the right (2).) Without getting too far into the mechanical details, it would seem that Mo’s having a little bit more trouble stepping forward with the right leg than with the left.

In effect, in picture (1) his left leg is flexed because it’s waiting for the trailing right leg to catch up. And if you look at the orientation of his forearms, you can see that the right elbow (1) is far more flexed than the left (2), mimicking, to almost a perfect degree, the angle of the opposite knee in each of the pictures.

The point is that it wouldn’t matter where you look at the piston system (of an internal combustion engine) from. Whether you observe the piston system from the frame of reference of the piston head, the main axis of the crankshaft, or the counterweights, you would see that the entire system is balanced. Each counterweight remains perfectly opposite to a piston, and the pistons remain perfectly opposite to each other.

This is so important that much of what makes sports cars—particularly “traditional” sports cars like Ferraris—and race cars cost as much as they do is the technology to keep the engine block balanced to the picogram. The better this is accomplished, the more torque can go through the engine without breaking apart the block.

Mo Farah is not some amateur. For the past few years, he has set the highwater mark for excellence in distance running up to the 10,000 meters. And even then there are differences.

Why is this happening? The “big” answer to this question probably isn’t in some esoteric discussion of biomechanics. Quite simply, the 10,000 meters are run on an oval track, and this is the final stretch. For more than 24 laps, he’s been turning into his left leg. It’s probably a lot more tired than his right, so it’s having a harder time supporting his body during stance. (Hence the flexion).

If we asked Mo to keep running for a few more laps (not that he would) we’d find that his right leg would continue to trail a little more, and his left leg would flex even further. If you look at the video you’ll see that even down the final stretch he’s compensating quite well by driving forward with his right shoulder every step.

But as he becomes more tired, we’d see that this strategic compensation stops being enough. We’d probably observe his left foot taking increasingly longer to leave the pronation (flattening) that occurs during the stance phase. The supination (pointing) which occurs towards the end of the stance phase, would come too little, too late, possibly creating a heel whip for the duration of the race.

pronation & supination.png
Pronation and Supination

As this is happening, the huge amount of forces that go into his body as his feet strike the ground will travel through it at increasingly odd angles. There is a potent compounding effect here: The more experienced, fitter, and more rested body aligns itself correctly with the forces of running. The less experienced, less fit, and tired body does not.

For the weekend warrior with the New Year’s resolution, running a marathon is biomechanically a far more hostile experience than it is for the skillful runner. Some people overpronate from the get-go. Others start with a tight hip. Over the course of 40,000 paces, this brings nothing but disaster.

Physics favors the trained runner much like the Greek Gods favored the heroes of mythology, by further increasing their already formidable advantages in battle. The skillful runner already comes into the race with stronger muscles, denser bones, a more resilient nervous system, and a more robust metabolism. As a final reward for their training efforts, the impact forces of running fall into place and work with them, not against.


7 thoughts on “The Running Gait, Part 1: Contralaterality”

  1. Hi Ivan, thanks for the very interesting insight into biomechanics and physics of running. I guess this why you say that “no pain – no gain” saying only apply to an unbalanced and unsynchronized body… it makes sense!!
    My questions are:
    How could I check if my bodily movements are or are not perfectly contralateral when walking/running?
    Should they be synchronized up to the picogram in order to be perfectly efficient?
    How can I re-align and re-balance (tune-in) my movements?
    Is it a matter of conscience and will in training or are there other means?


    1. Well, first off, you can’t really be balanced to the picogram. For those of us who are adults, one side of our body is volumetrically larger (and also heavier) than the other side. And then there’s all of our idiosyncrasies: whichever shoulder we hang our backpack on, or even whichever hand we like to carry a glass of water on, our body will think of our opposite leg and hip as the “provider of support” for that function. So, the more functions one leg provides support for, the more it will develop muscle and bone mass.

      And because adults have grown into this—we’ve bent down to pick up thousands of objects with one leg supporting most of our weight and the other slightly flexed behind us, our body’s “pattern of thought”—that a particular leg is the provider of support—is now manifest as more muscle and bone mass.

      The point here is that many instances of asymmetrical pain or discomfort (on one hip, one knee, etc.) could have to do with the fact that our body has “grown into” its ideas of what one leg is for and what the other hand is for (it’s usually, but not always, the other hand). So, it’s not enough to, say, simply do more squats with one leg than the other. While that will fix the problem superficially by causing the lighter side to become heavier, it does little to fix the underlying problem, which is that the heavier side is heavier because the brain thinks of it as the main provider of support.

      So, this means that the simplest way to solve this problem is also the most functional one, within reason. Just start doing stuff with the other side. Make a note of which leg you put in front (if you do so) when you squat down to pick up a box, and then practice doing the same with the other one. Sling your backpack over the opposite shoulder.

      If you want to get into more complex fine-tuning, I recommend that you practice with gait-based activities. Rule one: relax. And what you want to do is to focus on the ends of your limbs (your hands and feet) and start a mental metronome so that your limbs all switch directions to that metronome. As you do, you’ll notice that the arcs of movement of one hand is different than the other hand (and elbow and shoulder), and that the same goes for the legs. But starting with the metronome, and starting with the endpoints (hands and feet) without really worrying about the knees or the shoulders is the place to start. And your body, if it has reasonably few muscle imbalances, will tend to organize itself accordingly.


  2. Hello. In my limited experience of filming people running, just about everyone over strides more on the right leg with a later pull on the left and sometimes a more bent posture when landing on the right. There is often more of a heel strike on the right. Interestingly, I noticed my young son’s shoes wearing down more on the right heel from his very first pair of walkers. Coincidence? Presumably this is due to differences in strength, as you say, none of us are identical on each side. I guess most people are right handed…so are they over striding to favour the right leg because the left is relatively weak? Do you have any insight on this? Thanks, Anne.


    1. Anne:

      What you’re most likely looking at is simple lateral dominance. (I’m going to expand on this for a later post, by the way).

      Let’s suppose you’re right handed (like 80% of people). If you’re throwing a spear right handed, this means that all the force of the throw is supported by the opposite (left) leg. So, actually, if you’re right handed the left leg is often (but not always) going to be stronger.

      This doesn’t counter your observation, though: if the left leg is stronger, that means that they can create a longer stride when they’re being supported by their left leg. So, the RIGHT leg has a chance of reaching forward farther, because their left can support them longer. This means that the right heel strike becomes more emphasized.


      And the other result is that the right leg is not as accustomed to supporting the body as the left (whether this is strictly speaking “strength” or “ability” doesn’t really matter to this conversation). So you get a little bit more flexion because (a) it either doesn’t have the strength not to flex as much, or (b) because it takes slightly longer to catch the body because it’s marginally less powerful.

      And this is strictly about when the legs are working right. When there’s a problem (functional dominance isn’t a problem), what on the surface looks as the correct function can sometimes be part of the issue.


      1. Thanks for your reply, very interesting. Is it well recognised then that the left leg is often stronger in right handed people? I guess that would perhaps tally with a more bent posture in right leg stance. Excuse my ignorance I’m just working this lot out. How does a stronger left leg create a longer stride? Is it because it can support a bigger angle of fall? You often see upper body rotation towards the right presumably counterbalancing the differences in stride…or facilitating them? If there is a big difference in overstride and much upper body rotation does this predispose one to injury, or is any difference fine so long as you are relaxed and allowing the body to balance itself. I would have thought a big difference between left and right and excessive upper body rotation would be bad. I’m afraid I don’t quite get your point about flexion a weaker right leg. Isn’t it less flexed on landing if you are overstriding more? Thanks again, Anne


      2. Anne:

        Yes, essentially it is the angle of fall. And think not of the extension of the leg upon strike, but of the implications of having a leg extended: it means that you were falling off of your other leg that much more, which means that you’re coming into the ground with that much more force.

        In order to absorb that shock, you often need to go into greater flexion.

        So it’s not so much that the right leg is necessarily “weaker” in terms of pure strength than the left leg in right handed people, but rather that the forces of landing are relatively greater for the right leg than the left leg.

        So, it may have been bad for me to frame it as a question of “strength” per se. It is really a question specifically of function: if you’ve trained your left leg to support you during right-handed throwing, lifting, etc. (which is invariably what happens), then your body programs the left leg as the leg you “fall off of” and the right leg as the leg you “fall on to.” You can see this in an extreme example in martial artists: it’s quite common for them to get knee injuries in the “falling off of” leg, because most injuries occur during landing, and the leg (but really, the whole body) doesn’t quite know how to perform the function.

        And the body essentially counterbalances in order to facilitate something; if the upper body didn’t rotate, you’d see that rotational force stop at the knee, for example, in which case you’re creating lateral knee pain.

        Does this help?


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